Summary of Work: For some elements, use of toenail levels as a surrogate measure of exposure may provide an estimate of exposure superior to that made on the basis of data from food frequency questionnaires, hair, blood levels, or other measures. Toenails reflect exposure over a longer period of time than do blood or urine measures, and are less likely to be influenced by contaminantion than hair. We hypothesize that toenail levels may provide a good measure of exposure for a group of elements (Ca, Mg, Fe, Zn, Cu, Mn, Se, Mo, Cr, Co, Hg, and Al), that has a purported link with chronic disease. Improved methods of asssessing exposure to these elements will facilitate studies of their adverse or beneficial health effects. Repeated samples of whole-diet homogenates and toenails were collected over a one-year period from 77 subjects. The element content of diet and toenail specimens is being determined by neutron activation analysis and graphite furnace atomic absorption. After the concentration of the trace elements in the toenails and diet specimens has been determined, we will examine how well the toenail level of each element reflects intake. We will also compare the estimates of intake based on nails with those obtained with a standard food-frequency questionnaire to see which is better.